1. Aerial Photography

2. Introduction A “bird’s eye view” is very useful for map making
Features obscure each other less when viewed from above than when viewed from ground level
Air photography can come from many sources
Airplanes of all types can be equipped with cameras
So can hot air balloons, helicopters, pigeons, etc.
We’ll discuss primarily film cameras, but most of the same concepts also apply to digital cameras

3. Basic Terminology
Focal Length – the distance between the camera lens and the film
Flying Height – the height of the plane (and therefore the camera) above the ground
Nadir – the point on the ground directly below the camera
Flight Line – the path of the airplane over which a sequence of pictures is taken
Stereoscope - a device used to view/measure feature heights and/or landscape elevations using pairs of air photographs
Fiducial Marks – marks on photographs used to align adjacent photos for stereoscopic analysis

4. Air Photo Scale Scale (RF) = 1 : (focal length / flying height)
Focal length and flying height should be in the same units
Example:
Focal length = 6 inches
Flying height = 10,000 ft
Scale = 0.5 / 10,000 = 1:20,000
Ray, R.G. (1960) Aerial Photographs in Geologic Interpretation and Mapping. Geological Survey Professional Paper 373.

5. Basic Camera Everything above “C” is inside the camera
The film sits on the film plane
f = focal length
H = Elevation above ground
ACB = angle of coverage
Scale: RF = 1/(H / f)

6. Basic Camera Film exposure:
The quantity of energy that is allowed to reach the film
Controlled by relative aperture (f-stop) and shutter speed, as well as energy source
f-stop, or relative aperture
f / effective lens diameter

7. Film Basics Types of film Black and White (a.k.a. panchromatic) Color
Infrared
Color Infrared (CIR)

8. Basic Color Theory Additive Color Subtractive Color
Colors of light Colors of pigment
(e.g., on a computer monitor) (e.g., paint)

9. Film and the Electromagnetic Spectrum

10. CIR Films

11. Resolution
Currently, a 9 x 9 inch format digital camera would require about 400 million pixels to approach the resolution of a typical 9 x 9 inch film camera (Paine and Kaiser 2003).
This is roughly 2222 pixels/inch.

12. Flight Lines
Successive photos on a flight line typically have ~60-65% overlap to allow stereoscopic viewing
Adjacent flight lines typically have ~20-30% overlap
Some location of the ground may be imaged on 3 photographs along the same flight line and 6 photographs in total

13. Stereoscopic Parallax
Stereoscopic Parallax is caused by a shift in the position of observation
Parallax is directly related to the elevation / height of features

14. Air Photo Mosaic

15. Stereopair

16. Stereoscope

17. Aligning Air Photos Fiducial marks
Type and number vary amongst cameras
4-8 marks (e.g., top, bottom, left, right, & 4 corners)
Principal Point (PP) - the exact point at which the camera was aimed when the photo was acquired
Conjugate Principal Point (CPP) – the principal point of an adjacent photograph in the flight line

19. Sources of Distortion From Collection: Natural:
Yaw – plane fuselage not parallel to flight line
Think about having to steer your car slightly into a strong cross wind
Leads to pictures not being square with the flight-line
Pitch – nose or tail higher than the other
Leads to principal point not being at nadir
Roll – one wing higher than the other
Natural:
Haze
Topographic changes
For example, if flying over mountains, the height above the ground will a) change from picture to picture, and b) not be uniform in a single picture. Both of these lead to irregularities in the photo scale